This invention relates to a portable fastener driving tool and, more particularly, to a fastener driving tool which may be operated in either a sequential mode or a contact mode of operation.
Portable fastener driving tools are conventionally used in the construction industry to deliver nails or other type of fasteners into a work piece. These fastener driving tools are trigger actuated, and the triggers are usually provided with mechanisms to prevent firing of the tool under certain operating conditions. These fastener driving devices or tools typically include a housing defining a fastener drive track, a magazine assembly carried by the housing for receiving a supply of fasteners and feeding successive fasteners into the drive track, a fastener driving element mounted within the drive track for movement through repetitive cycles each of which includes a fastener drive stroke in one direction which a fastener within the drive track is engaged and moved outwardly of the drive track into the work piece, and return stroke. A drive piston is operatively connected with the fastener driving element for movement therewith and a trigger is carried by the housing and is constructed and arranged for movement from a normal, inoperative position into a operative position for initiating movement of the piston and the fastener driving element through a fastener drive stroke.
To insure that the trigger will not be actuated to drive the fastener until the tool is in engagement with the work piece, a conventional contact trip mechanism is employed which is carried by the housing adjacent a nose piece of the tool. The conventional contact trip is disposed so as to extend beyond the nose piece of the tool and must be depressed by engagement of the tool with the work piece in order for the tool to be fired in a contact mode. The contact trip includes a portion which is cooperable with a trigger lever such that movement of the trigger lever is totally prevented until the contact trip engages the work piece. Thus, the tool is prevented from being fired until the contact trip is engaged with the work piece. These conventional fastener driver tools do not require any particular operating sequence between the trigger and the contact trip mechanism. It is typically only necessary that the bottom contact trip be engaged and the trigger pulled before the tool can be fired.
In certain circumstances, it has been desired to prevent the tool from firing when the contact trip is engaged inadvertently when the trigger is pulled. For instance, when an operator is handling the tool and inadvertently bumps the contact trip when the trigger is held in the pull position, the tool will fire.
Various devices have been developed which will ensure that the tool will not be fired unless a proper operating sequence is followed. One of these mechanisms is disclosed in U.S. Pat. No. 4,629,106 to Howard. Howard discloses an actuating mechanism which permits the tool to be repeatedly fired by engagement of the contact trip mechanism, but once the trigger is subsequently released, the actuating mechanism must be recycled with the bottom contract trip mechanism actuated before the trigger is operated to permit another fastener to be driven. The trigger includes a push-button arrangement for permitting the tool to be fired in a contact or bottom trip mode. Thus, when the bottom trip mode is required, the button is moved inwardly before or after the trigger has been pulled. Thus, once the button has been moved inwardly, contact of the bottom trip mechanism when the trigger is depressed will fire the tool. However, this mechanism is subject to a deficiency in that the contact mode may be selected by inadvertent movement of the button when the trigger is not pulled. Thus, if the button is inadvertently moved inwardly and thereafter the trigger is pressed, inadvertent contact of the contact trip will fire the tool. Further, due to the structure of the conventional device, double actuation of the tool may occur inadvertently during the sequential mode of operation. Double firing or actuation of the tool, as herein defined, occurs when more than one cycle of tool operation results when only a single operating cycle is intended.